1. Field of the Invention
The present invention relates generally to the field of propulsion systems for watercraft, such as pleasure craft, fishing boats, pontoon boats, ski boats, and so forth. More particularly, the invention relates to a technique for adjusting trim in a propulsion system employing dual electric motor drive units.
2. Description of the Related Art
Various propulsion systems have been proposed and are currently in use for watercraft, such as pleasure craft and fishing boats. Such propulsion systems may typically be classified as either internal engine-based systems, or electric motor-based systems. In the first class, an internal combustion engine is operatively connected to a prop to produce a thrust used to propel the boat through the water. Systems of this type include conventional outboard motors and inboard motors.
Electric drives, commonly referred to as trolling motors or electric outboards, typically include an electric motor which is energized to rotate at various speeds to drive a prop. In a conventional configuration, the electric motor and prop are provided in a propulsion unit which is submerged when the motor is deployed. Directional orientation of the propulsion unit, through a manually or remotely rotatable support tube, determines the direction of the resultant thrust, and thereby the direction of navigation of the boat.
While propulsion systems of the foregoing types are suitable for many applications, they are not without drawbacks. By way of example, internal combustion engines are simply inappropriate for certain activities, such as fishing, due to their noise and thrust levels. Trolling motors and electric outboards offer quiet and controllable navigational devices, but also have fairly limited controllability, particularly directionally due to the need to rotate the devices during use. The conventional trolling motors are also subject to damage upon contact of submerged objects, and may become entangled in weeds and plant growth as the boat is displaced in shallow waters.
A novel propulsion system has been proposed that includes a pair of propulsion units spaced from one another and secured to a boat hull. The propulsion units each include a variable speed electric motor and a prop rotated by the motor during operation. By coordinating the rotational speeds of the motors, components of a desired resultant thrust may be generated by the units to navigate the boat in various directions. The system offers considerable advantages over heretofore known propulsion systems, including inherent controllability, reduced maintenance and deployment times, inherent protection from submerged objects, and so forth.
In coordinating the control of dual electric motor drive units, a particular challenge resides in trimming the coordinated drives to provide accurate navigational control. For example, due to the direction of rotation and geometries of the individual props, a net resultant thrust may be generated which is not aligned with the longitudinal centerline of the watercraft hull, even when a control unit provides a nominal xe2x80x9cstraight-aheadxe2x80x9d navigational command. Such variances may also result from tolerances in the geometry of the hull, the angular position of the propulsion units, speed control of the motors, and so forth.
There is, at present, a need for a technique designed to trim a dual electric motor propulsion system of the type described above. There is a particular need for a system which offers a very straightforward and simple mechanism for trimming the drive, available both to service personnel and to boat owners.
The invention provides a technique for trimming a dual electric motor propulsion system designed to respond to these needs. The technique offers a straightforward series of steps for adjusting a null or nominal steering signals provided to electric motors of the propulsion system to allow for navigation in a desired direction, such as parallel to the centerline of the craft. By setting a calibration value or offset in the trim technique, tolerances and variations in the physical and electrical systems are compensated, offering predictability in both the nominal or null directional control, as well as in other navigational settings on either side of a straight-ahead setting.
The technique may be implemented in any of a variety of ways. In a present embodiment, for example, an operator may enter a calibration sequence and navigate the boat in the desired direction manually. When the boat is tracking properly, as determined by the operator, a calibration setting is sensed and stored for later reference. The trigger for storing the calibration setting may be a switch provided at an operator""s console or foot pedal control input device. The trim setting is then referred to in generation of output control signals to account for the calibration or offset required to provide predictable navigational control.